bunch of config, will see ...

config/sync/migrate_plus.migration.d7_flaglistitems.yml

@@ -0,0 +1,47 @@
+uuid: 89876565-2aff-4ee8-b911-d0dc90115044
+langcode: en
+status: true
+dependencies: {  }
+id: d7_flaglistitems
+class: null
+field_plugin_method: null
+cck_plugin_method: null
+migration_tags:
+  - 'Drupal 7'
+  - Content
+migration_group: d7_materio
+label: 'Materio Flag List Items D7'
+source:
+  plugin: d7_flaglistitems_materio
+process:
+  user_id:
+    plugin: migration_lookup
+    migration: d7_users
+    source: uid
+  type: entity_type
+  flag_list:
+    plugin: migration_lookup
+    migration: d7_flaglists
+    source: fid
+  baseflag: baseflag
+  entity_id:
+    plugin: migration_lookup
+    migration:
+      - d7_node_materiau
+      - d7_node_article
+    no_stub: true
+    source: entity_id
+  name:
+    plugin: concat
+    source:
+      - flagcolname
+      - dest_entity_id
+    delimiter: ' '
+destination:
+  plugin: 'entity:flag_list_item'
+migration_dependencies:
+  required:
+    - d7_users
+    - d7_node_article
+    - d7_node_materiau
+    - d7_flaglists